1. Field of the Invention
This invention relates generally to a monitoring apparatus for training devices and more particularly to such a monitoring apparatus which is adapted to select one of a plurality of training devices and to monitor an audio signal transmitted therefrom.
2. Description of the Prior Art
In a so-called LL (Language Laboratory) system, in order to permit an instructor or teacher to observe the progress of many trainees or students, each of which is trained in a booth provided with a respective training device, the instructor monitors one-by-one, for example, through a pair of headphones or the like, audio signals, such as, the pronunciation of various words or phrases by the several trainees, transmitted from the respective booths to a monitoring apparatus provided at a control desk for the instructor. Such an apparatus is disclosed, for example, in Laid-open Japanese Patent Publication No. 60-15076.
FIG. 1 shows a monitoring system according to the prior art, wherein tape recorders including respective audio signal amplifiers A.sub.11 to A.sub.mn are located in N booths arranged in a matrix having m rows and n columns, that is, N =m.times.n. Audio signals, such as, the pronunciation of words and phrases in a foreign language by the several trainees, are collected by microphones M in the respective booths and are supplied to the monitoring apparatus provided on the control desk for the instructor. The monitoring apparatus is shown to include audio signal input terminals 1.sub.-1,1.sub.-2,. . .,1.sub.-N and control circuits or switches 2.sub.-1,2.sub.-2, 2.sub.-N, each of which corresponds to a respective one of the N booths. Output signals from the control circuits 2.sub.-1,2.sub.-2,. . .,2.sub.-N are all supplied to a monitor amplifier 3, and the output signal from the latter is supplied to a pair of headphones HP through an output terminal 4 for monitoring by the instructor. A shift register 9 is supplied with an output signal from a pulse generator 11 through a selector circuit 12, and respective output signals from the shift register are supplied to the control circuits 2.sub.-1,2.sub.-2, 2.sub.-N in an order according to a scanning command signal from a scanning direction change-over circuit 13. Such scanning command signal is indicative of a desired scanning direction, that is, the forward direction or backward direction, so that the output signals from amplifiers A.sub.11 to A.sub.mn corresponding to the respective trainees are supplied one by one to the monitoring apparatus. Thus, the instructor can monitor, one by one, the progress of each trainee. The monitoring apparatus according to the prior art is further shown to have a manual scanning change-over circuit 14 having a push button adapted to be momentarily depressed for causing the pulse generator 11 to be temporarily inhibited from generating its normal pulsed output signal, and for causing one scanning command pulse signal indicative of the forward direction or the backward direction to be supplied to shift register 9 through selector circuit 12 so that the instructor monitors the trainee in the booth next to that which was previously monitored. If the above-mentioned push-button is kept depressed, the period of inhibition of the output signal from pulse generator 11 is made to be a predetermined period of time by an output signal from change-over circuit 14, that is, pulse generator 11 issues successive pulses with an increased period therebetween, so that the instructor can successively monitor the several trainees one at a time for the predetermined or increased period of time.
By the way, in using the described language laboratory system, a plurality of training programs are prepared for trainees having different levels of skill, and the trainees are classified into a number of groups, in accordance with their respective skills or degrees of advancement. The monitoring apparatus is provided with a group selector switch and a program selector switch (not shown), which supply the control circuits 2.sub.-1,2.sub.-2,. . .,2.sub.-N with suitable control signals so that the instructor can successively monitor trainees who belong to the same group or who study the same program.
However, when the monitoring apparatus has its control circuits 2.sub.-1,2.sub.-2,. . .,2.sub.-N supplied with various control signals as described above, the control circuits in the monitoring apparatus, as well as peripheral circuits including the network between the control desk and the several booths become complicated. Further, the number of control keys is increased, so that the instructor's operation of the control keys of the monitoring apparatus is complicated and made difficult.
To solve this problem, it has been proposed that the N booths be divided into groups by row or column, with trainees in the same row or column having the same skill level or degree of advancement, and thus using the same study program.
In Japan, it is the tendency to arrange the booths in groups by the column. Therefore, it is sufficient if the instructor can monitor the trainees one by one in a selected column.
On the other hand, in countries foreign to Japan, the booths are, in many cases, grouped by row. It is therefore impossible to employ, in a country foreign to Japan, an unmodified monitoring apparatus intended for use in Japan. For this reason, at the time of manufacture, the scanning direction for successive monitoring has to be changed from the column direction to the row direction by the use of a bit switch or the like provided in the monitoring apparatus. Therefore, the monitoring apparatus for use in Japan and those for export from that country, must be carefully distinguished from each other during production and during preparation for shipping.